Epoxy compounds are used for a variety of purposes, by utilizing a ring-opening of a 1,2-epoxide oxirane ring. In particular, bisphenol A-type epoxy resins and novolak-type epoxy resins are commonly used as semiconductor encapsulating materials, due to their mass productivity and low cost, as well as their excellent heat resistance and water resistance.
The conventionally-known epoxy compounds are mainly produced by reacting phenolic hydroxyl-containing compounds with epihalohydrins. However, epoxy compounds produced by such methods contain organic halogens. From the viewpoint of reliability, it has therefore been difficult to use them as encapsulating materials for highly-integrated semiconductors in recent years. For this reason, great effort is being made toward development of methods for producing halogen-free epoxy compounds, without using epihalohydrins as starting materials, one of which involves oxidation of a carbon-carbon double bond of olefins with oxidizing agents.
Common methods for oxidation of olefins for providing epoxy compounds include methods using heavy metal compounds, or nitric acid, m-chloroperbenzoic acid or the like as oxidizing agents, as well as industrial methods using oxidizing agents, such as peracetic acid or performic acid.
However, since reactions using nitric acid or peracetic acid are dangerous, special equipment is necessary for actual production. Moreover, these oxidizing agents have high oxidizing power and are very dangerous, and several explosions have occurred in the past.
On the other hand, hydrogen peroxide is inexpensive and non-corrosive, and produces either no post-reaction by-products, or only water, and therefore the environmental load is low and it serves as an excellent oxidizing agent for industrial use. Conventional methods that are known for producing epoxy compounds from olefins, by using hydrogen peroxide as an epoxidizing agent, include methods using an aqueous hydrogen peroxide solution for epoxidation in the presence of quaternary ammonium chloride, phosphoric acids and a tungsten metal salt (see Patent documents 1 and 2 below), methods using an aqueous hydrogen peroxide solution for epoxidation with a phase-transfer catalyst, such as a quaternary ammonium salt, with tungstic acids and α-aminomethylphosphonic acid, as catalysts in an organic solvent (see Patent document 3 below), methods of reacting olefins and hydrogen peroxide in a toluene solvent, in the presence of tungstic oxide prepared from a tungsten compound and an aqueous hydrogen peroxide solution, a quaternary ammonium hydrogen sulfate salt and phosphoric acids (see Patent document 4 below), methods of epoxidation using a multicomponent oxidation catalyst comprising a tungsten compound, a quaternary ammonium salt, phosphoric acids and/or boric acids and a hydrogen sulfate salt (see Patent document 5 below), and methods of epoxidation in a chloroform solvent using a catalyst having both phase-transfer capability and epoxidizing capability, such as a cetylpyridinium salt of a heteropolyacid (see Non-Patent document 1 below).
In addition, methods that employ acetonitrile in an epoxidizing reaction using hydrogen peroxide have been known for years (see Non-Patent document 2 below). Since epoxidation by these methods is a milder reaction than conventional methods, and the reaction occurs under a basic condition, there is little decomposition of generated epoxy groups. However, white solid acetamide is generated as a by-product, and it is difficult to separate and remove the acetamide from the target product (epoxy compound). This is because the acetamide and the target product are both organic materials, and thus, if an appropriate solvent is not selected, it may not be possible to remove the acetamide by rinsing. In addition, it is difficult to carry out purification by distillation due to the acetamide being in a solid state at ambient temperature, and scaling-up is difficult in the case of column purification. Furthermore, since the method disclosed in Non-Patent document 2 employs an alcohol-water based reaction solvent, solvent exchange, which is carried out as pretreatment to extract the target epoxy compound product into an organic solvent, makes it necessary to concentrate a reaction mixture while hydrogen peroxide remains therein, and when methanol is used as the solvent, for example, this can potentially lead to concentrating of an organic peroxide derived from hydrogen peroxide, such as methyl peroxide, which results in a very dangerous situation when the process is scaled-up.